Treatment of magnesite ores



PatentedNov. 21, 1944 i TREATMENT OF MAGNESITE'ORES Arthur J. Weinig, Golden, 0010., assignor to Basic Magnesium, Incorporated, a corporation of Nevada No Drawing.

- 13 Claims.

This invention relates to a method of separating the constituents of magnesite ores and the like, and more particularly relates to froth flotation methods of separating constituent minerals of magnesite ores.

The present application is based in part on the disclosure in my co-pending' application, Serial No. 394,851, filed May 23, 1941, for Separation of magnesite ore constituents, and relates to certain improvements in the process therein described, Features described but not claimed here-. in have been made the subject matter of claims in my co -pending application.

Magnesite ores are magnesium carbonate compositions (MgCOa) containing serpentine, dolomite, hydro-magiiesite, forsterite or the like, as contaminants, and are found in various deposits throughout Canada and the United States, such as those at Luning, Nevada, for example.

For analytical purposes these ores may be classifled according to lime content, magnesium oxide content and insoluble content. In my earlier ap- Application February 12, 1942, Serial No. 430,619

plication, Serial No. 394,851, I have disclosed methods of recovering two grades of products by froth flotation, in which the primary product contained not. to exceed 1% insoluble matter and not to exceed 1% lime (CaO) The secondary product of such separations which also was suitable for industrial purposes contained 1%-2% insoluble matter and 1 /2-2% CaO.

However, in the treatment of certain types of material, the reagents of the aforesaid application will produce insufficient quantity of first grade product, and an excessive amount of reject material.

This condition apparently is due to the tendency of contaminant slimes to pass into the froth formed by the reagent and thus contaminate the final products.

It is an object of the present invention to increase the selectivity of reagents used in the froth flotation treatment of magnesite ores;

Another object of the invention is to provide methods of restraining the tendency of contaminant slimes to pass into the froth along with the valuable constituents in froth flotation treatments of magnesite ores.

Other objects reside in novel steps and treatments, all of which will appear more fully in the course of the following description.

In practicing the present invention, the ore is first reduced to a suitable degree of fineness, av 100 mesh product serving as a standard, preferably by wet grinding in closed circuit with 'a classifier.

In any event the ground ore is mixed with a liquid carrier vehicle, usually water, to form a free flowing pulp. The pulp is then subjected to a conditioning treatment in the presence of certain reagents. If desired, the reagents may be introduced into the grinding circuit, although preferably separate conditioning tanks will be used between the grinding and flotation circuits.

In preferred practice, ametallic salt is introduced into the pulp and this is followed with the addition of alkali to insure complete reaction and dispersion of reagent materials before the pulp is passed into the flotation stage.

In such treatments fatty acid compositions serve as collectors, while the metallic salts promote the action of such collector reagents. A hydroxide hydrogel is formed as a reaction product of the metallic salt and the alkali introduced into the pulp in the manner previously described and this hydrogel or hydroxide also is used to assist the separation, functioning as a depressant or inhibitor for lime-bearing constituents, such as dolomite, or insolubles such as serpentine.

It is not necessary to maintain an alkaline circuit although good results are obtained thereby, but a pH of 6 or slightly higher has been found sufficient when basic salts, or hydroxides are formed.

Frother reagents may be employed in the treatment if desired, and pine oil and synthetic alcohols are cited as suitable for this purpose.

Conjointly with or following the introduction of the collector reagent, the pulp is subjected to aeration, usually accompanied by mechanical agitation, in any suitable flotation cell or series of cells, and as a result, the magnesite content is selectively carried to the surface in a froth where it may be removed by overflow or otherwise.

When desired, the tailings of this first separation are passed to a second flotation stage, where in the presence of additional reagent, a second froth of market grade and of a different grade than the first froth is collected.

The improvement which comprises the present invention resides in the discovery that pyrophosphate compositions, such as a tetra-alkali pyrophosphate, or other similar alkali salts of molecularly dehydrated phosphoric acid, inmprove the recovery and restrain the passage of contaminant slimes into the froth product. Sodium, potassium, or ammonia tetraphosphate are suitable for this purpose. Certain typical tests will illustrate the efficiency and economy of the present invention.

Ore from a Luning, Nevada, deposit was crushed to 5 inch maximum size and passed over a 2% inch screen. That part of the ore which did not pass the 2 inch screen was hand-picked into two grades and the low grade portion was remixed with the minus 2 inch portion. The mixture of coarse low grade ore and of fine ore was used as flotation feed. Thi mixture contained a relatively high proportion of slimy contaminant with the result that the quality of the froth product from a flotation separation was seriously impaired.

This is illustrated by the following pilot-mill test: The ore containing the slime contaminant was ground in a rod mill in closed circuit with a classifier to 100 mesh. The classifier overflow, which consisted of 2 parts water to 1 part ore,

was subjected to flotation with the following reagents: 8.46 #/T of aluminum sulphate, 2.62 #/T of caustic soda, and 3.14 #/T of lauric acid. The pH of the pulp after the addition of the reagents was 8.3.

The results of this test are shown below:

It may be readily observed that this test produced only 31% of concentrate and that the grade of the concentrate does not fall in either of the ranges specified as desirable.

I will now disclose another test which will illustrate the beneficial effect of adding tetrasodium pyrophosphate to both the rougher and cleaner cells of the pilot mill. All other conditions in the pilot mill were held constant, including the pH value of the pulp.

In order that the pH value of the pulp might remain at the value 8.3, it was necessary to allow the tetra sodium pyrophosphate in the pulp to replace a part of the caustic soda. It is well to maintain a constant pH value in comparative tests so that the frothing power of an equal amount of lauric acid will be the same in each The results of this test are shown below:

Per cent Per cent Per cent Pmdu m of feed insoluble 080 139 100 2.28 2. 47 81 43 .62 .se Telling s 57 a. 51 3. 72

Upon comparing this test with the test wherein no tetra sodium pyrophosphate was used, it will be seen that the use of tetra sodium pyrophosphate is responsible not only for improving the grade of the concentrate, so that it now lies in the better of the two specified compositions,

but also for an increase of 12% in the amount of concentrate.

In addition to the purely metallurgical improvement which resulted from the use of tetra sodium pyrophosphate, there was a marked improvement in the ease with which theoperation of the mill could be controlled. Since there is no visual method of estimating the efficiency of a magnesite beneflciation, it is important that the flotation process used to affect thebeneficiation be capable of maintaining itself in a condition of eflicient equilibrium for reasonable periods of time.

Therefore, since experience indicates that the tetra sodium pyrophosphate aids in maintaining uniform operating conditions in the pilot mill, the use of tetra sodium pyrosphosphate may be considered as a substantial improvement from the operational point of view as well as from the' metallurgical point of view. I

Further testing has demonstrated that with ores treated by the methods of my aforesaid application where the final products have been only of a grade having between 1.5% and 2% CaO, the addition of the sodium tetraphosphate has served to bring about approximately a 70% recovery of concentrate having between 1% and 1.5% 09.0

content. 7

Thus it is apparent that by adding relative minor quantities of a pyrophosphate composition, such as a tetra-alkali pyrophosphate or an alkali tetraphosphate at only nominal increase in operating cost, a much larger recovery of valuable products is obtained.

It will be understood that while specific tests have been cited, the various reagent combinations of my'aforesaid application may be used in con-' junction with the present invention and improved grade and recovery will result from the introduction of a tetra-alkali pyrophosphate.

Likewise, the various operating procedures specified in my aforesaid application, including the hydrogel formation resulting from combining an alkali with iron or aluminum salts in the pulp, may be employed within the spirit and scope of the present invention. In this connection, it will be understood that soaps may be employed in place of fatty acids as the collector reagent, and the caustic may be either a hydroxide or a basic salt.

Basic salt as used in the description and claims is employed in the sense stated in Websters New International Dictionary, 1927 edition, namely: Having the base-forming constituents present in excess of the proportion necessary for a normal compound; as basic salts.

What I claim and desire to secure by Letters Patent is:

1. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an'operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a hydrogel-forming salt selected from .the group consisting of iron and aluminum salts, and ina magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction productof an alkali and a hydrogel-forming salt selected from the group consisting of iron and aluminum salts, and introducing an alkali salt to molecularly dehydrated phosphoric acid into such pulp to reduce the floatability of contaminant slimes therein.

3. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a hydrogel-forming salt selected from the group consisting of iron and aluminum salts, and introducing a tetra, alkali pyrophosphate composition into such pulp to reduce the floatability of contaminant slimes therein.

4. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a hydrogel-forming salt selected from the group consisting of iron and aluminum salts, and introducing sodium tetraphosphate into such pulp to reduce the floatability of contaminant slimes therein.

5. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a hydrogel-forming salt selected from the group consisting of iron and aluminum salts, and introducing potassium tetraphosphate into such pulp to reduce the floatability of contaminant slimes therein.

6. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a hydrogel-forming salt selected from the group ducing ammonia tetraphosphate into such pulp to reduce the floatability of contaminant slimes therein.

7. In the treatment of magnesite ores, in which a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprise-s maintaining the pulp at a pH value of 6 or higher, retarding the passage of contaminant slimes into the froth concentrate of such an operation by having a hydroxide hydrogel present in the pulp which is a reaction product of an alkali and a a magnesite ore pulp containing a collector reagent of soap-like character is subjected to a froth flotation treatment for the recovery of magnesite constituents'of the ore as a froth concentrate separate from the dolomite constituents of the ore, the improvement which comprises adding a quantity of pyrophosphate to promote the collecting action of the reagent.

9'. The method of concentrating magnesite ores by flotation, ,which comprises filming magnesite particles in a magnesite ore pulp with a collector reagent comprising a composition of soap-like character, forming a hydrogel in the pulp as the reaction product of an alkali and a hydrogelforming salt selected from the group consisting of iron and aluminum salts introduced therein, subjecting such pulp to aeration in the presence of a frothing agent to collect the magnesite content of the pulp as a froth concentrate, and retarding the passage of contaminant slimes into said froth concentrate by having a pyrophosphate composition present in the pulp during aeration.

10. The process of concentrating the magnesite constituents of magnesite ores, separate from the lime-bearing and insoluble constituents of such ores, which comprises introducing magnesite ore in finely divided condition into a liquid. carrier vehicle to form a pulp, forming a hydroxide hydrogel in the pulp as the reaction product of an aluminum salt and an alkali supplied thereto, entering an alkali salt of molecularly dehydrated phosphoric acid into the pulp, and subjecting the resulting pulp intermixture to,aeration in the presence of a lauric acid collector reagent to selectively carry the magnesite constituents to the surface in a froth.

11. The process of concentrating the magnesite constituents of magnesite ores, separate from the lime-bearing and insoluble constituents of such ores, which comprises introducing magnesite ore in finely divided condition into a liquid carrier vehicle to form a pulp, forming a hydroxide hydrogel in the pulp as the reaction product of an aluminum salt and an alkali supplied thereto, entering an alkali salt of molecularly dehydrated phosphoric acid into the pulp, and subjecting the resulting pulp intermixture to aeration in the presence of a fatty acid collector reagent to selectively carry the magnesite constituents to theconsisting of iron and aluminum salts, and introores, which comprises introducing magnesite ore in finely divided condition into a. liquid carrier vehicle to form a pulp, forming a hydroxide hydrogel in the pulp as the reaction product of an aluminum salt and an alkali supplied thereto; entering a tetra alkali pyrophosphate composition into the pulp, and subjecting the resulting pulp intermixture to aeration in the presence of a collector reagent of soap-like character to selectively carry the magnesite constituents to the surface in a froth.

13. The process of concentrating the magnesite constituents of magnesite ores, separate from the lime-bearing and insoluble constituents of such ores, which comprises introducing magnesite ore in finely divided condition into a. liquid carrier vehicle to form a pulp, forming a hydroxide hydrogel in the pulp as the reaction product or an aluminum salt and an alkali supplied thereto, entering tetra sodium pyrophosphate into the pulp, and subjecting the resulting pulp intermixture to aeration in the presence 01.9, lauric acid collector reagent to selectively carry the magnesite constituents to the surface in a froth.

ARTHUR J. WEINIG. 

